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Gold Tin Solder Paste Application

Gold Tin Solder Paste Application: Soldering is an important technique in the assembly of electronic products. To make a sound solder joint, the choice of solder materials is very important. Solder ability, melting point, strength, Young’s modulus, thermal expansion coefficient, thermal fatigue, creep properties and creep resistance will affect the quality of a solder joint.

Solders are generally described as fusible alloys with liquidus temperature below 400° C (750°F). The elements commonly used in solder alloys are tin (Sn), lead (Pb), silver (Ag), bismuth (Bi), indium (In), antimony (Sb) and cadmium (Cd). In addition to tin-lead alloys, binary solder alloys include tin-silver, tin-antimony, tin-indium, tin-bismuth, lead-indium and lead-bismuth. Ternary alloys include tin-lead-silver, tin-lead-bismuth and tin-lead-indium.

 Gold Tin Solder Paste Application

Gold-tin solder paste is used in a variety of high-reliability applications, where its high melting point, non-creep, high-tensile stress, thermal and electrical conductivity, as well as proven usage life makes it a standard "known-good" material.

Nanoshel Gold Tin solder paste is formulated for automated high-speed, high-reliability, single or multi point dispensing equipment. It also functions well in hand-held applications. Highly accurate volumes can be dispensed using either pneumatic or positive displacement devices. Optimal dispensing performance is dependent on storage conditions, equipment type, and set up.

Nanoshel Gold Tin solder paste (80Au/20Sn) has a melting point of 280°C (556°F). It can be made into solder paste form with various options to address specific applications. Gold-tin solder paste is generally used in applications that require a high melting temperature (over 150°C), good thermal fatigue properties and high temperature strength. It is also used in applications that require a high tensile strength and high corrosive resistance or in step soldering applications where the paste will not melt during a subsequent low-temperature reflux process. For these reasons, Nanoshel Au/Sn solder paste is widely used in military, aerospace and medical applications.

PROPERTIES OF GOLD TIN SOLDER PASTE

Some principal physical properties of Au/Sn solder paste are in table, by which the advantages of Au/Sn solder could be identified as follows:

Properties
Density 14.7 g.cm-3
Coefficient of thermal expansion 16×10-6 /° C
Thermal Conductivity 57 W.m-1K -1
Tensile Strength 275 MPa
Young’s modulus 68 GPa
Shear Modulus 25 GPa
Poisson’s ration 0.405
Electrical resistivity 16.4 × 10-8 ?.m
Elongation 2 %[/su_table]

The alloy has high yield strength at ambient temperature and even at assembly temperatures of 250-260 °C, it is still strong enough to maintain hermeticity. Material strength is comparable to that of high temperature brazing materials, but with the benefit of much lower processing temperatures.

Good wet ability; meanwhile, due to similar compositions, Au/Sn solder has a good compatibility with Au metallization due to low leaching rate to thin Au coatings; no migration problems like Ag etc.

Low viscosity; the alloy has low enough viscosity in liquid form that it can fill large gaps. In addition, Au/Sn solder has high corrosion creep resistances good thermal and electrical conductivities. The disadvantages of Au/Sn solder include high cost, brittleness, low elongation and difficult to process.

Gold Tin Solder Paste Application: Au/Sn SOLDER PASTE

Nanoshel Au/Sn eutectic alloy has a melting temperature of 280°C high strength, Flux less, high thermal and electrical conductivity, good wet ability, low viscosity, good solder ability, high corrosion and creep resistance. It has been widely used in the applications in lid sealing and component attachment of ceramic packaging for microelectronic and optoelectronic components Au/Sn can dramatically increase the reliability and thermal/electrical conductivity for the packaging of these components.

Au/Sn Solder paste is used in die bonding (high brightness LEDs, peltier elements and power semiconductors) for vehicle installations, lightings, thermoelectric exchange modules and others. Also in sealing (crystal devices and SAW devices) for mobile communications, base stations, MEMS sensors and others.

Since eutectic Au/Sn has a much higher melting point than Sn96.5Ag3.5 solder (280 °C versus 221 °C), it is incompatible with the organic materials widely used with electronic packaging. However, many high-reliability solder applications exist where the unique combination of mechanical and thermal requirements make eutectic Au/Sn the optimal choice. These applications include, but are by no means limited to, lid sealing, RF and DC feed-through attach on optoelectronic packaging, and laser diode die attach.

Au/Sn solder must be applied properly to get good joining results. The main effects to the joints quality include: Au/Sn solder composition, surface quality of work pieces and preforms (for instance, oxides, contamination and flatness, etc.), processing conditions (like furnace temperature profile, peak temperature, forming gas and tools).

As a hard solder alloy, the alloy also becomes very attractive to flip-chip bonding where the active area of the device is next to sub mount. In this case, a solder alloy like Au/Sn with good thermal and electrical conductivities is particularly needed. Au/Sn performs also have applications in microwave systems assembly and other fields. With the superior properties of Au/Sn and the advantages of using preforms, Au/Sn will become more popular and even necessary in packaging applications

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